Mankind's Explanation:

A Cometís Odd Orbit Hints at Hidden Planet

Far
beyond the solar systemís nine known planets, a body as massive as Mars may
once have been part of our planetary system and might still be there.

Although the proposed planet would lie too far away to be seen from
Earth, its gravitational tug could account for the oddball orbit of a large
comet spotted in the outer solar system a year ago.

Known as 2000 CR105, the comet moves about the sun in a much
more elongated pathway than originally though, astronomers now find.
Observations over the past year by Brett Gladman of the Observatoire de la Cote
díAzur in Nice, France, and his colleagues show that the cometís orbit takes
it further than 200 astronomical units (AU) from the sun and as close as 44 AU.
One AU equals the Earth-sun distance of about 150 million kilometers.

Such an oblong orbit is usually a sign that an object has come under the
gravitational influence of a massive body. But 2000 CR105, which mat
be an escapee from the distant reservoir of comets known as the Kuiper belt,
never gets anywhere near any of the solar systemís familiar team of nine
planets. Even at its closest approach to the sun, the approximately 400 km wide
ball of ice comes no closer than 14 AU to Neptune, the nearest known candidate
for a significant gravitational interaction.

The astronomers concede that feeble and random pushes from Neptune could
have slowly nudged 2000 CR105 into its current orbit. However,
preliminary analysis suggests this scenario isnít likely, note Gladman,
Matthew Holman of the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Mass., and their collaborators.

In an article the researchers recently posted on the Internet (http://arXiv.org/abs/astro-ph/0103435),
they suggest that a massive body lurking among the tiny, frozen residents of the
Kuiper belt could have been the culprit.

That object could have been Neptune itself. According to one theory,
Neptune and Uranus first formed between the orbits of Jupiter and Saturn and
were then flung out to greater distances from the sun.

If that kick propelled Neptune into the Kuiper belt before it settled
into its current orbit nearly circular orbit, its gravity could have caused the
orbits of several objects like 2000 CR105 to stretch into elongated
trajectories.

Alternatively, the cometís orbit could be the handiwork of an as-yet
unseen planet whose mass lies somewhere between that of the Earthís moon and
Mars, the researchers say. Itís likely that such an object would have
coalesced in the outer solar system from the same debris that formed Neptune,
Uranus, and the cores of Jupiter and Saturn, Holman notes.

Thereís only a 1 percent chance that a planet could have survived in
the Kuiper belt or its surroundings over the 4.5 billion year age of the solar
system, says Holman. If the planet found a secluded nook of the belt, however,
it could remain intact today.

If the proposed planet is as massive as Mars, it would have to lie some
200 AU from the sun about 7 times Neptuneís distance Holman calculates. Were
it closer, observers would have stopped it.

A planet lurking in the Kuiper belt now or in the past might also explain
why many members of the belt have orbits away from the plane in which the nine
known planets orbit the sun.

ďUndoubtedly, something [massive] knocked the hell out of the belt,Ē
says Harold F. Levison of the Southwest Research Institute in Boulder, Colo.
ďThe question is whether it is there now.Ē

The stability of the orbit of 2000 CR105 suggests that any
planet that influenced the cometís path has long since departed. If
astronomers find a family of objects similar to 2000 CR105, the
nature of their orbits could indicate whether the hidden planet is in fact still
there, Levison says.